Flow cytometry is a generic term describing a technique for rapidly analyzing and separating biological cells as they flow in single file through laser beam. Light scattering is used with these instruments for cell sizing and for detecting changes in cell morphology. The rapid growth of this field has led to the introduction of these multiparameter cell sorters into laboratories where they are used by researchers unfamiliar with light-scattering measurements. Calculations and experiments will be used to characterize the scatter detector responses of several commercial cell sorters, as well as other research instruments in terms of sensitivity to changes in cell diameter, nuclear-to-cytoplasmic diameter ratio, extinction coefficient, cell orientation, and internal structures. In parallel with these studies, an attempt will be made to identify and separate cells from normal and abnormal heterogeneous cell populations obtained in peripheral blood based on inherent cellular differences, as well as differences occurring as a result of histochemical and immunochemical markers. If these studies are successful, we will work with the medical staff at the University of New Mexico School of Medicine to evaluate patient care applications of these techniques.